The purpose of this project is to study the brain dysfunctions underlying declining mental health and cognitive deterioration in the elderly using neurometric (EEG and AER) assessment techniques. Recent research by E.R. John, et al, has revealed neurometric deficits which suggest the existence of at least 4 cluster analysis subgroups within the heterogeneous population of impaired elderly. The objective of this project is to replicate and extend these important results. In phase 1, neurometric data will be obtained from 210 elderly outpatients (150 mildly-moderately impaired and 60 normal controls) following preliminary behavioral and psychometric screening. The purpose of phase 1 is to replicate the previous results and to determine the test-retest reliability of the neurometric assignment to the normal or impaired groups and to particular cluster subgroups. In phase 2, the significance of the neurometric clusters, in terms of behavioral impairment and etiology or brain pathology, will be determined by relating the neurometric deficits and clusters to patterns of deficit on behavioral and medical-neurological measures. Up to 30 randomly selected phase 1 patients from each major cluster will be given an extensive battery of cognitive and neuropsychological tests, behavioral ratings, and medical-neurological measures (including a CAT scan). Some specific hypotheses concerning the nature of the subgroups will be examined, and the stability of cluster membership over time will also be evaluated. The results will provide new insights concerning the brain dysfunctions underlying age-related mental decline. The successful specification of subgroups may lead in subsequent research to identification of treatments which are differentially effective for specific subgroups.